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1999, Cisco Systems, Inc.www.cisco.com

Module 6:WAN Basics

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6-2CSE: Networking FundamentalsWAN Basics 1999, Cisco Systems, Inc.www.cisco.com

Agenda

WAN Basics

Transmission Options

WAN Requirements &

Solutions

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WAN Basics

1999, Cisco Systems, Inc. www.cisco.com

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4/366-4CSE: Networking FundamentalsWAN Basics 1999, Cisco Systems, Inc.www.cisco.com

A network that serves users across a broadgeographic area

Often uses transmission devices providedby public carriers (Pacific Bell, AT&T, etc.)

This service is commonly referred to asplain old telephone service (POTS)

WANs function at the lower three layers ofthe OSI reference model

Physical layer, data link layer, and networklayer

What Is a WAN?

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WAN Devices

WAN Switch Switches traffic such as Frame Relay,X.25, and SMDS, and operates at thedata link layer

Modem Interprets digital and analog signals,

enabling data transmission overtelephone lines

Access Server A concentration point for dial-in anddial-out connections

CSU/DSU Adapts a terminal physical interface to a

switch interface in a switched-carriernetwork

ISDN Terminal Connects ISDN Basic Rate Interface(BRI) to other interfaces, such asEIA/TIA-232

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WAN Terminating Equipment

Modem

Data Terminal EquipmentDTE

Data Circuit-Terminating Equipment

The Service ProvidersEquipment

DCE

EIA/TIA-232V.35X.21HSSI

To CorporateNetwork

The Customers

Equipment

WAN Provider(Carrier) Network

Physical Cable Types

Usually on the

CustomersPremises

Router

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Dedicated physical circuit established, maintained,and terminated through a carrier network for eachcommunication session

Datagram and data stream transmissions

Operates like a normal telephone call

Example: ISDN

WANModem Modem

Circuit Switching

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Network devices share a point-to-point link totransport packets from a source to a destination

across a carrier network

Statistical multiplexing is used to enable devices toshare these circuits

Examples: ATM, Frame Relay, SMDS, X.25

WAN

Modem Modem

Multiplexing Demultiplexing

Packet Switching

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A logical circuit ensuring reliablecommunication between two devices

Switched virtual circuits (SVCs)

Dynamically established on demand Torn down when transmission is complete

Used when data transmission is sporadic

Permanent virtual circuits (PVCs)

Permanently established

Save bandwidth for cases where certainvirtual circuits must exist all the time

Used in Frame Relay, X.25, and ATM

WAN Virtual Circuits

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OSI Reference Model

PhysicalLayer

DataLink

Layer

Network Layer

LLCSublayer

MACSublayer

S

MDS

X.21bis

EIA/TIA-232EIA/TIA-449V.24 V.35

HSSI G.703EIA-530

HDLC

PPP

WAN Protocols

LAPB

X.25PLP

FrameRela

y

SDLC

WAN Protocols

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SDLC IBMs SNA data link layer communicationsprotocol

HDLC Bit-oriented synchronous data link layer protocol

LAPB Data link layer protocol in the X.25 protocol stack

PPP Provides router-to-router and host-to-networkconnections over sync and async circuits

X.25 Defines connections for remote terminal accessand computer communications in PDNs

ISDN Permits telephone networks to carry data, voice,

and other source traffic

Frame Relay Switched data link layer protocol that handlesmultiple virtual circuits using HDLC; replacingX.25 due to higher efficiency

WAN Protocols

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TransmissionOptions


T i i O ti WAN

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Transmission Options or WANServices

Type of Service Analog or Digital Permanentor Temporary

POTS

ISDN

Leased line T1/E1

Frame Relay

X.25

Analog

Digital

Digital

Digital

Digital

Temporary

Permanent

Temporary

Permanent

Permanent

DSL Digital Temporary

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POTS Using Modem Dialup

Widely available

Easy to set up

Dial on demand

Asynchronous transmission

Low cost, usage-based

Lower bandwidth access requirements

Telecommuters

Mobile

Users

Modem

Corporate Network

Server

ModemAccess Router

BasicTelephone

Service

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Integrated Services DigitalNetwork (ISDN)

High bandwidth

Up to 128 Kbps per basic rate interface

Dial on demand

Multiple channels Fast connection time

Monthly rate plus cost-effective,usage-based billing

Strictly digital

LANServer

Company Network

Telecommuter/After-

Hours, Work-at-Home

BRI2B+D

BRI/PRI23B+D

30B+D (Europe)

ISDN

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ISDN

One physical connectionto the ISDN network

23 logical connections

(U.S./Canada) 30 logical connections

(Europe)

Used at central site

Primary Rate Interface (PRI)

1.536Mbps

23B

30B

D

64 Kbps

64 Kbps}

One physical connectionto the ISDN network

Two logical connections

Used at remotetelecommuter site

64 Kbps

64 Kbps

16 Kbps

144Kbps

2B

D}

{

Basic Rate Interface (BRI)

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Leased Line

One connection per physical interface Bandwidth: 56 kbps1.544 Mbps

T1/E1 and fractional T1/E1

Cost effective at 46 hours daily usage

Dedicated connections with predictablethroughput

Permanent

Cost varies by distance

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Frame Relay

Permanent, not dialup

Multiple connections perphysical interface(permanent virtual circuits)

Efficient handling ofbursty (peak performanceperiod) data

Guaranteed bandwidth(typical speeds are

56/64 Kbps, 256 Kbps,and 1.544 Mbps)committed informationrate (CIR)

Cost varies greatly by region

Permanent Virtual Circuit (PVC)

Connecting Offices with Frame

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Free If

Available

Traffic

Time

Peak

CIRWhat YouPay For {

{

FrameRelay

Connecting Offices with FrameRelay

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X.25

Very robust protocol for low-quality lines

Packet-switched

Bandwidth: 9.6 kbps64 kbps

Well-established technology;large installed base

Worldwide availability

X.25DCE

DTE DTE

DCE

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DSL

Modem

End User

DSL

Modem

DSL

DSL is a pair of modems on each end of a copper wire pair

DSL converts ordinary phone lines into high-speed data conduits

Like dial, cable, wireless, and T1, DSL by itself is a transmission

technology, not a complete end-to-end solution End-users dont buy DSL, they buy services, such as high-

speed Internet access, intranet, leased line, voice, VPN, and videoon demand

Service is limited to certain geographical areas

Copper Loop

Ethernet ATM

Digital Subscriber Line (xDSL)

Server

CorporateNetwork

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DSL TechnologyMax. Data Rate

Down/Uplink (bps)Line CodingTechnology

BasebandVoice?

VDSLVery-high-data-rate DSL

5155M / 1.62.3M13M / 1.62.3M

TBD Yes

ADSLAsymmetric DSL

8M / 1M1.5M / 640K

CAP, DMT,G.lite

Yes

IDSLISDN DSL

144K / 144K 2B1Q No

SDSLSymmetric DSL

768K / 768K 2B1Q/CAP No

HDSL2High-data-rate DSL

1.5M2M / 1.5M2M(T1E1 Symmetric)

OPTIS No

Trade-off is reach versus bandwidth

Reach numbers are best-case assuming clean copper

Different Layer 1 transmission technologies, need acommon upper protocol layer to tie them together

Max. ReachFeet (km)

1,000 (0.3)4,500 (1.5)

18,000 (5.5)

18,000 (5.5)+(w/repeaters)

22,000 (6.9)

15,000 (4.6)

Key Attributes

Very fastShort reachNo standard yet

Coexists with POTSTechnology of choice

for residential

Uses existing ISDN CPERelatively slow

SymmetricNo standard

Standard still underdevelopment

DSL Modem Technology

Asynchronous Transfer Mode

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Asynchronous Transfer Mode(ATM)

Technology capable of transferring voice, video, anddata through private and public networks

Uses VLSI technology to segment data, at highspeeds, into units called cells

5 bytes of header information 48 bytes of payload

53 bytes total

Cells contain identifiers that specify the data streamto which they belong

Capable of T3 (44 Mbps), E3 (34 Mbps), and SONETtransmission speeds (OC-1 at 51.84 Mbps to OC-12+)

Primarily used in enterprise backbones or WAN links

DataHeader

5 48

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??

Which Service?

Before deciding,determine the answersto some questions: Will employees use the Internet

frequently? Will the Internet be used for

conducting business?

Is a large volume of trafficbetween branch offices of the

business anticipated? Is videoconferencing or video

training needed betweenlocations?

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How Services Stack Up

Frame Relay 56,000 bps to 45,000,000 bps

ISDN BRI 56,000 to 128,000 bps

ISDN PRI 1,544,000 bps

T1/E1/DS1 1,544,000 bps/2,090,000 bps

Analog modems 33,600 bps

56K modems 56,000 bps

Cable modems 30,000,000 bps

ADSL modems 9,000,000 bps

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Wide-Area NetworkRequirements


Wide-Area Network

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Wide Area NetworkRequirements

Minimize bandwidth costs

Maximize efficiency

Maximize performance

Support new/emerging applications

Maximize availability Minimize management and maintenance

Multiservice consolidation

Bandwidth efficiency

Performance and QoS guarantees

Emerging IP services

Carrier-class reliability

Ease of operation and management

Manage Bandwidth to

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Manage Bandwidth toControl Cost

Dial-on-demand routing

Bandwidth on demand Snapshot routing

IPX protocol spoofing

Compression

SoftwareCosts 2.7%

HardwareCosts 8.0%

Transmission Costs87.8%

Maintenance1.5%

Source: Data Communications

Dial on Demand Routing

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Dial-on-Demand Routing

Dials connection only when needed

Ideal for low-volume, periodic traffic

Controls usage costs

InterestingTraffic

Remote SiteMain OfficePSTN

Bandwidth-on-Demand

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Adds bandwidth when needed Configurable thresholds

Controls usage costs

Bandwidth-on-Demand

Start FileTransfer

Remote SiteMain Office PSTN

S h t R ti

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ISDNRouting

Table

Routing

Table Link Up

Update Request

Routing Updates

RoutingTable

Updated

Controls exchange of routing updates

Client initiates request

Server responds

Snapshot Routing

IPX P t l S fi

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IPX Protocol Spoofing

Without spoofing

With spoofing

LAN traffic can be very chatty

WAN links are expensive

Solution: Limit unnecessary traffic across WAN

High overhead traffic

across WAN

Spoofing SpoofingMuch reduced overheadacross WAN

Compression

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Compression

Three typesHeader

Link

Payload

Van Jacobson header compression

RFC 1144

Reduces header from 40 to ~5 bytes

Compression

Data

Data

CRC

CRC

TCP/IP Header

hdr

Dial Backup

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Dial Backup

If a primary link goes down or is too busy

Load balancing

Completely customizable

Secondary

Primary

Autodial

DSU/CSUX

WAN Summary

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Operate beyond the local LANs control

Customers pay telephone service providersfor WAN connections such as ISDN, xDSL,

Frame Relay, leased line, X.25, etc. Switching methods include point-to-point,

circuit switching, packet switching,dialup, and WAN virtual circuits

Key devices include WAN switches,access servers, modems, and CSU/DSUs

Bandwidth optimization features areessential for controlling WAN costs

WAN Summary

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06 WAN Basics

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